Amphiphilic polymers are one example of the polymers used in emulsifying agents, dispersing agents, capsules, and coating agents, for example. As the general structure of an amphiphilic polymer, there are random copolymers and block copolymers.
In random copolymers, the arrangement of the hydrophilic monomers and the hydrophobic monomers is not controlled, leading to a polymer chain that has poor efficiency at adsorbing to interfaces. In contrast, in block copolymers the hydrophilic monomers and hydrophobic monomers are arranged in a systematic manner and thus the polymer chain has an excellent ability to adsorb to interfaces. However, the large molecular weight of each segment does not allow the polymer chain to adhere closely, and as a result, satisfactory adsorption cannot be obtained.
In view of these matters, a brush-shaped amphiphilic alternating copolymer made of a vinylbenzyl-terminated polystyrene and a methacryloyl-terminated polyethylene oxide has been developed (see non-patent document 1 and non-patent document 2). This was arrived at by examining the various conditions for copolymerizing a vinylbenzyl-terminated polystyrene (PS-VB) with a methacryloyl-terminated polyethylene oxide (PEO-MC), and it was found that adding SnCl4 to this copolymer system resulted in the formation of a PEO-MC/SnCl4 complex that can be copolymerized with the PS-VB to obtain an alternating copolymer. In this alternating copolymer, a one-to-one charge transfer complex in which the PS-VB is the donor and the PEO-MC/SnCl4 complex is the acceptor is formed, and it is thought that a homopolymer of the one-to-one charge transfer complex of these two is occurring. The amphiphilic alternating copolymer made of PS-VB and PEO-MC has side chains off a main chain that are high-density and incompatible with one another, and takes on a brush-shaped structure with a high aspect ratio. Further, the amphiphilic side chains are oriented alternately at the interface and thus the structure has excellent adsorption ability and adsorption density.
Non-Patent Document 1: K. Ishizu, X. X. Shen and K Tsubaki, Polymer, 41 2053(2000)
Non-Patent Document 2: K. Tsubaki, H. Kobayashi, J. Satoh and K. Ishizu, J. Colloid Interface Sci., 241, 275(2001)